2,763 research outputs found
Direct Identification of Northern Sage-grouse, Centrocercus urophasianus, Nest Predators Using Remote Sensing Cameras
The status and apparent decline of Sage-grouse (Centrocercus spp.) has been of increasing concern and lower nesting success could be contributing to population declines. Our objective was to directly identify Sage-grouse nest predators. Following visual confirmation of radio-marked Sage-grouse nest establishment in 1997-1999, we installed automatic 35 mm cameras controlled by an active infrared monitor. Of 26 nests monitored by cameras, 22 successfully hatched and four were unsuccessful. American Elk (Cervus canadensis), Badger (Taxidea taxus), and Black-billed Magpie (Pica hudsonia) destroyed three of the four unsuccessful nests, and domestic cattle caused abandonment of the fourth. Richardson’s (Spermophilus richardsonii) and Thirteen-lined Ground Squirrels (S. tridecemlineatus) were recorded at nests, but were not detected in predation
Preliminary Evidence Of SFAS No. 130's Effect On Gains Trading In The Insurance Industry
Gains trading represents a form of earnings management whereby appreciated marketable securities are sold at a gain while those with a loss are retained. By not requiring unrealized gains and losses on available-for-sale securities to flow through income, SFAS No. 115 failed to close the door on this type of earnings management. With SFAS No. 130, however, these unrealized gains and losses must now be reported prominently in a financial statement as a component of comprehensive income. By examining the level of gains trading for a sample of companies in the insurance industry both before and after the implementation of SFAS No. 130, the current study provides evidence suggesting that this form of earnings management subsided subsequent to the adoption of SFAS No. 130
Heisenberg models and a particular isotropic model
The Heisenberg model, a quantum mechanical analogue of the Ising model, has a
large ground state degeneracy, due to the symmetry generated by the total spin.
This symmetry is also responsible for degeneracies in the rest of the spectrum.
We discuss the global structure of the spectrum of Heisenberg models with
arbitrary couplings, using group theoretical methods. The Hilbert space breaks
up in blocks characterized by the quantum numbers of the total spin, and
, and each block is shown to constitute the representation space of an
explicitly given irreducible representation of the symmetric group ,
consisting of permutations of the spins in the system.
In the second part of the paper we consider, as a concrete application, the
model where each spin is coupled to all the other spins with equal strength.
Its partition function is written as a single integral, elucidating its
-dependence. This provides a useful framework for studying finite size
effects. We give explicit results for the heat capacity, revealing interesting
behavior just around the phase transition.Comment: 16 pages LaTeX, one of the 2 figures included as a postscript file.
Oxford preprint OUTP-93-18S, to be published in Phys. Rev.
NUTRITONAL CONDITION OF ADULT FEMALE SHIRAS MOOSE IN NORTHWEST WYOMING
The "animal indicator concept" assumes that because an animal is a product of its en­vironment, it likely reflects the quality of its environment. Although this concept has been applied to assess population condition and habitat quality for Alaskan moose (Alces alces gigas), to our knowledge this is the first time it has been used to assess the nutritional status of a Shiras moose (A.a. shirasi) population. We investigated the physical condition and nutritional status of adult (≥ 2 years) female Shiras moose captured in northwest Wyoming during the winters of 2005-2007. Rump fat depth was measured via ultrasonography and biological samples were collected and analyzed for hematology, serum chemistry, micro- and macronutrients, endo- and ectoparasites, and bacterial and viral serology. Five blood parameters believed to be important predictors of moose condition (packed cell volume, total serum protein, hemoglobin [Hb], calcium [Ca], and phosphorous [P]) were compared to data from Alaskan moose considered to be in average-above average condition. Micro- and macronutrient values were evaluated based on published deficiency levels for domestic herbivores. We conducted a correlation analysis to determine if a significant relationship existed between hematological and serum chemical parameters and rump fat depth. Mean rump fat depth did not differ among years and was greater than reported values for Alaskan moose. However, a high proportion of sampled moose had Hb, Ca, and P values lower than Alaskan moose that were considered to be in average condition. Hair and serum micro- and macronutrient analyses indicated a high proportion of moose were potentially deficient in copper, zinc, manganese, and P. We observed a marginally significant relationship between depth of rump fat and two serum chemical parameters (aspartate amimotransferase and lactate dehydrogenase). The results are suggestive of a Shiras moose population in marginal physical condition that is probably related to less than optimal habitat quality. These findings should assist managers in evaluating the health of Shiras moose populations throughout their range
Quarantine generated phase transition in epidemic spreading
We study the critical effect of quarantine on the propagation of epidemics on
an adaptive network of social contacts. For this purpose, we analyze the
susceptible-infected-recovered (SIR) model in the presence of quarantine, where
susceptible individuals protect themselves by disconnecting their links to
infected neighbors with probability w, and reconnecting them to other
susceptible individuals chosen at random. Starting from a single infected
individual, we show by an analytical approach and simulations that there is a
phase transition at a critical rewiring (quarantine) threshold w_c separating a
phase (w<w_c) where the disease reaches a large fraction of the population,
from a phase (w >= w_c) where the disease does not spread out. We find that in
our model the topology of the network strongly affects the size of the
propagation, and that w_c increases with the mean degree and heterogeneity of
the network. We also find that w_c is reduced if we perform a preferential
rewiring, in which the rewiring probability is proportional to the degree of
infected nodes.Comment: 13 pages, 6 figure
Graph Partitioning Induced Phase Transitions
We study the percolation properties of graph partitioning on random regular
graphs with N vertices of degree . Optimal graph partitioning is directly
related to optimal attack and immunization of complex networks. We find that
for any partitioning process (even if non-optimal) that partitions the graph
into equal sized connected components (clusters), the system undergoes a
percolation phase transition at where is the fraction of
edges removed to partition the graph. For optimal partitioning, at the
percolation threshold, we find where is the size of the
clusters and where is their diameter. Additionally,
we find that undergoes multiple non-percolation transitions for
Power Law of Customers' Expenditures in Convenience Stores
In a convenience store chain, a tail of the cumulative density function of
the expenditure of a person during a single shopping trip follows a power law
with an exponent of -2.5. The exponent is independent of the location of the
store, the shopper's age, the day of week, and the time of day.Comment: 9 pages, 5 figures. Accepted for publication in Journal of the
Physical Society of Japan Vol.77No.
Secondary Lead Poisoning in Golden Eagle and Ferruginous Hawk Chicks consuming Shot Black-tailed Prairie Dogs, Thunder Basin National Grassland, Wyoming
Recreational shooting of black-tailed prairie dogs (Cynomys ludovicianus) is a common activity at Thunder Basin National Grassland (TBNG), Wyoming. The prairie dog carcasses left in the area are scavenged by coyotes (Canis latrans), raptors, and other animals. These scavengers are susceptible to lead (Pb) poisoning if they consume Pb bullet fragments or Pb shot when scavenging the shooter-killed prairie dogs. In 2000, a local rehabilitator noted an increase of Pb poisoning cases in raptors (L.Layton, pers. comm. 3/30/01) from the area. We collected several shooter-killed prairie dog carcasses from TBNG for determining if Pb fragments remained embedded in the tissue that potentially would be consumed by raptors. Radiographs showed fragments consistent with Pb to be present. In 2002, we conducted a more in-depth study to determine if Pb poisoning was occurring in raptors at TBNG by documenting the number of raptors on prairie dogs at colonies where shooting occurred, assaying bullet fragments in shot prairie dogs to determine Pb content, and analyzing blood and feather samples of ferruginous hawk (Buteo regalis) and golden eagle (Aquila chrysaetos) nestlings and feathers from burrowing owls (Athene cunicularia) for clinical signs of Pb poisoning.
We observed raptors foraging at prairie dog colonies and collected data on the number of shooters shooting at prairie dog colonies. To determine if raptors preferred foraging on shot prairie dogs, we compared raptor use at prairie dog colonies where shooting occurred to raptor use at prairie dog colonies where shooting did not occur. Shooter intensity did not predict raptor use. We also collected prairie dog carcasses and examined them for Pb shot fragments. We detected metal fragments in four of ten prairie dog carcasses. The total weight of the fragments found in each carcass ranged from 10 – 146 mg. Copper was the primary metal detected in 3 of 4 carcasses; but, significant amounts of Pb (20 mg, 28 mg, and 124 mg) were found in the three carcasses. Blood Pb concentrations in ferruginous hawk nestlings were below sub-clinical levels at TBNG and the control site near Rawlins, Wyoming. Analysis of red blood cell delta-aminolevulinic acid dehydratase activity, hemoglobin levels, and protoporphyrin levels also did not indicate Pb poisoning in ferruginous hawk nestlings. Additionally, blood and feather samples from golden eagle nestlings and feather samples from burrowing owls (juveniles and adults) at TBNG did not indicate Pb poisoning. Although ferruginous hawks and golden eagles (and possibly burrowing owls) scavenge on the carcasses of shot prairie dogs and some carcasses contained Pb-bullet fragments, we did not detect Pb poisoning in any of the birds. Lead poisoning may become important if the availability of alternate food sources decreases or shooter intensity increases
Exact perturbative solution of the Kondo problem
We explicitly evaluate the infinite series of integrals that appears in the
"Anderson-Yuval" reformulation of the anisotropic Kondo problem in terms of a
one-dimensional Coulomb gas. We do this by developing a general approach
relating the anisotropic Kondo problem of arbitrary spin with the boundary
sine-Gordon model, which describes impurity tunneling in a Luttinger liquid and
in the fractional quantum Hall effect. The Kondo solution then follows from the
exact perturbative solution of the latter model in terms of Jack polynomials.Comment: 4 pages in revtex two-colum
Modeling bursts and heavy tails in human dynamics
Current models of human dynamics, used from risk assessment to
communications, assume that human actions are randomly distributed in time and
thus well approximated by Poisson processes. We provide direct evidence that
for five human activity patterns the timing of individual human actions follow
non-Poisson statistics, characterized by bursts of rapidly occurring events
separated by long periods of inactivity. We show that the bursty nature of
human behavior is a consequence of a decision based queuing process: when
individuals execute tasks based on some perceived priority, the timing of the
tasks will be heavy tailed, most tasks being rapidly executed, while a few
experiencing very long waiting times. We discuss two queueing models that
capture human activity. The first model assumes that there are no limitations
on the number of tasks an individual can hadle at any time, predicting that the
waiting time of the individual tasks follow a heavy tailed distribution with
exponent alpha=3/2. The second model imposes limitations on the queue length,
resulting in alpha=1. We provide empirical evidence supporting the relevance of
these two models to human activity patterns. Finally, we discuss possible
extension of the proposed queueing models and outline some future challenges in
exploring the statistical mechanisms of human dynamics.Comment: RevTex, 19 pages, 8 figure
- …